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## Swap too much control for too little
If your concern is that being able to control light would make your character(s) too powerful, but you feel that not affecting light would seem like an oversight, you could consider making their effects on light undesirable - a weakness rather than a strength. You already have powers that become unstable when a psionic tries to do too much:

> However the larger in body the amount of air or gas the psionic user tries to grab, the harder it is to maintain, as well as it becoming more strenuous to hold onto

For example, a character may want to be stealthy, subtly affecting the electronics of a building in order to gain entry (perhaps by interfering with a security circuit or the power to an electromagnetic lock), but they cannot control the side effects. These may include electronic side effects, such as also affecting other nearby circuits, perhaps making all the lights in the building flicker on and off, or even directly affecting the path of the light already present, such as streetlight or moonlight. The building and its surroundings could appear to bend and distort as the light from it deviates from its usual straight line paths, almost like seeing something underwater.

To uninformed observers, this could be scary but meaningless, but to those experienced with dealing with psionics this would be an unmissable sign that someone is manipulating electricity nearby. As it affects the path of electromagnetic radiation directly, this distortion would also show up on cameras, whether security cameras or the smartphones of curious observers. Even if the owners were not expecting the building to be a target, news outlets and social media would soon make the side effects known around the world, making significant use of psionic power very risky for someone wanting to remain hidden.

All that power is only an advantage if the psionic can keep it concealed. They have little chance once they are known - they won't last long against a trained team in head to toe Faraday armour.

## Extending out from the visible electromagnetic spectrum
Unless your story requires this to only be a visible light effect, you could also have side effects that change the path of other electromagnetic radiation. 
- A psionic manipulating electricity in a hospital could cause x-rays taken in nearby rooms to be distorted.
- Random deviation of infra-red could makes parts of a room suddenly feel warmer or cooler when a psionic is operating in a nearby room ("I felt the room go cold. We were close").

## Proportionate size side effects
More powerful psionics may have a wider range of abilities, but less ability to hide or control their use, with a wider range of side effects. The size of the side effects may be in proportion to the amount of control exerted. At full power, the side effects may be so severe that the psionic cannot see what they are doing through all the light distortion, making their power a blunt instrument with no control over what it affects.

Large amounts of influence over electricity may cause large side effects, but even very small changes may cause large side effects if they require precision. Changing a value stored in a computer may require only a tiny amount of electricity at the point of change, but a huge amount of control to prevent surrounding stored values also changing. Wiping an electronic storage device could be easy, with little side effects, but changing a single value without leaving evidence of tampering could be very difficult, require years of practice, and still cause large widespread side effects in the surrounding environment - a light show that defeats the purpose of concealing the tampering if anyone is nearby to see it.

## Side effects even when not actively using power
There may even be small side effects just from the presence of a psionic, even when they are not trying to use their abilities. Stilling their powers completely may take deep concentration, meaning outside of that state they can be tracked and detected by their effects on things like magnetic compasses and digital displays (computer screens, phone screens, information screens in shops, airports, train stations, bus stops), and sometimes even subtle deviations in the path of ambient light, looking like the shimmer of distorted light over a hot road.